Simultaneous production of vinylaromatic compounds and arylacetylenes



Patented Mar. 8, 1938 1 UNITED STATES PATENT OFFICE SIMIULTANEOUS PRODUCTION OF VINYL- AROMATIC OOMPDUNDS AND ARYLACET- YLENES Robert a. Dreisbach, Midland, Mich assignmto The Dow Chemical Company, Midland,

Mich, a corporation of Michiga No Drawing. Application October 6, 1937, Serial No. 167,598

5 Claims. ,(01. 260 -168) radical, X and Y each represent hydrogen, halo-.

gen, or an alkyl radical containing not more than 3 carbon atoms, and n and n are integers having a sum not exceeding 5. The invention particularly concerns the simultaneous produc- 15 tion of styrene and phenylacetyleneby pyrolysis of one or both of the compounds isopropyl benzene and alpha-methyl styrene. Isopropyl benzene has heretofore been pyrolyzed at temperatures up to, but not exceeding 0 700 0., to obtain styrene and alpha-methyl styrene, but phenylacetylene has not been reported as a product of the reaction. In my own researches I have never obtained more than faint traces of phenylacetylene by pyrolyzing 25 isopropyl benzene at such temperatures.

However, I have found that isopropyl benzene may satisfactorily be pyrolyzed at higher temperatures to obtain not only the usual products, styrene and alpha-methyl styrene, but also 30 phenylacetylene in appreciable yield. In general,

the yield of phenylacetylene becomes higher and that of alpha-methyl styrene lower as the pyrolysis temperature is raised and by the use of temperatures above 900 C. the formation of alpha- 35 methyl styrene may practically be eliminated. I 1 have also found that the styrene and phenylacetylene, which boil together,'may readily be separated by distillation from any alpha-methylstyrene and unreacted isopropyl benzene present 40 and thatthe alpha-methyl styrene, alone or ad- .mixed with isopropyl benzene, may be further pyrolyzed to produce additional styrene and phenylacetylene. The phenylacetylene serves as an eifectiveagent for preventing polymerization 45 of the styrene, hence the mixture of these two compounds is a valuable and marketable prodnot. When desired, the phenylacetylene may be separated from the styrene by the chemical treatments hereinafter described. I

50 In. order to obtain phenylacetylene in appreciable yield, the pyrolysis is conducted at temperatures above 750 C. and below that at which excessive carbonizatlon occurs, preferably between 800 and 950 C. The pyrolysis may be 55 carried out in any of the usual ways, e. g. by

passing isopropyl benzene alone or in admixture with a gaseous diluent such as steam or carbon dioxide through an externally heated tube or a bath of-lead or other molten metal, but care must be taken to heat and promptly cool the vapors with suiilcient rapidity to avoid excessive carbonizatlon. In practice the pyrolysis is preferably carried out according to the general method for pyrolyzing alkylated aromatic hydrocarbons set forth in my co-pending application,

Serial No. 151,457, filed .July 1, 1937, of which this application is a continuation-in-part. This preferred mode of pperation, described below,

permits the desired products to be formed inv higher yield than I have found possible by the usual pyrolytic methods, without appreciable. carbonizatlon or tarring of the reaction mixture.

In my preferredmode of operation, liquid or vaporized isopropyl benzene and superheated steam are passed continuously into admixture with one another, the steam being employed in the proportion'and at the temperature required to attain the reaction temperature and furnish the heat of pyrolysis. Usually, between 7 and 10 parts by weight of steam superheated to a temperature between 800 and 1000 C. is used per part of isopropyl benzene, but the steam may of course be employed in other proportions and at even higher temperatures. The pyrolysis mixture is promptly cooled; e. g. by contact with water or passage through suitable heat exchangers or condensers, to a temperature below that at which rapid pyrolysis occurs, e. g. below 700 0., and the cooling is continued to condense the aromatic components ofthe mixture. The organic condensate is then distilled to collect as one fraction a mixture of styrene and phenylacetylene and as other fractions alpha-methyl styrene (when formed) and any unreacted isopropyl benzene. The alpha-methyl styrene may be collected as a final product or it may be returned, alone or in admixture with isopropyl benzene. to the pyrolysis for the formation of additional styrene and phenylacetylene.- As hereinbefore indicated, the phenylacetylene formed in the reaction distills together with the styrene and inhibits polymerization of the latter during manufacture, distillation, storage, and

shipment. Accordingly, this mixture of styrene of styrene and phenylacetylene with an aqueous.

ammoniacal solution of a salt of a metal belonging to group. 1, family 2, 'of the periodic system, e. g. silver chloride, silver sulphate, cuprous chloride, cuprous sulphate, etc., to precipitate the phenylacetylene as its metal salt, e. g. as silver or cuprous phenylacetylide. The ammoniacal metal salt employed in this treatment is preferably one containing the metal in its lowest valence.

The first of said methods for removing phenylacetylene is simple-and practicable, but does not permit recovery of the phenylacetylene as such. After said treatment the styrene is separated and purified by permitting the treated mixture to stand and stratify, separating the organic layer thereof, washing this layer free of acid with water or dilute aqueous alkali solution, and distilling the same, e. g. with steam or under vacuum.

The second of the above-mentioned methods for removing the phenylacetylene does permit recovery of the latter. After precipitating the phenylacetylene as its metal salt, the latter isv separated by filtration or decantation to recover the liquid styrene. 'The precipitate may then be acidified with a strong mineral acid, e. g. an aqueous sulphuric or hydrochloric acid solution, to regenerate the phenylacetylene. The latter forms a distinct layer and may be separated mechanically from the acid and purified by washing with water. The invention, accordingly, permits production of styrene and phenylacetylene either in admixture or as the individual compounds.

The following examples illustrate certain ways in which the principle or theinvention has been applied, but are not to be construed as limitin I the invention.

Example 1 Isopropylbenzene was passed, in continuous flow at a rate of approximately 50 grams per minute, first through a heated chamber wherein.

it was vaporized and preheated to about 285 C.

and thence into admixture with a current of steam superheated to approximately 825 C., the

[rate ofsteam flow being such that the mixture formed had a temperature of approximately 750 C. The vapor mixture was passed in less than 0.03 second through the mixing zone directly into condensers wherein it was rapidly cooled and condensed. The organic layer of the condensate was separated and dried. It contained approximately 45.4 per cent by weight of unreacted isopropyl benzene, 27.3 per centof-styrene, 14.8 per cent of alpha-methyl styrene, and 0.43 per cent 01' phenylacetylene.

Example 2 benzene vapors and approximately 205 pounds of highly superheated steam were passed in steady flow through a tubular iron reactor, wherein they formed a mixture having a temperature of 805 C. The time of passage was 1 hour 20 minutes. The mixture passed through the reactor and into suitable cooling apparatus at such rate as to be maintained at temperatures above 700 C. i'or'less than 0.05 second, probably about 0.03 second.

The mixture was cooled asit issued from the re- I styrene homologues.

actor suffl ciently to condense the aromatic produnreacted isopropyl benzene and some benzene.

Example 3 64.5 pounds of isopropyl benzene was gradually vaporized and the vapors were passed continuously into admixture with a stream of steam superheated to 890, C., the respective rates of flow being such that the mixture had atemperature of about 825 C. The time of passage'was 3 hours 30 minutes. The mixture was immediately cooled and condensed and the organic layer 0! the condensate was separated and dried as in Example 2. There was obtained 48.8 pounds of a liquid organic mixture containing approximately 52.8 per cent by weight of styrene, 9.3 per cent of alpha-methyl styrene, 8.5 per cent of phenylacetylene, and 12.5 per cent of unreacted isopropyl benzene, the remainder being largely benzene and ethylbenzene. The yields of styrene, alphamethyl styrene, and phenylacetylene were 52.6 per cent, 7 .9 per cent, and 8.1 per cent, respectively, based on the isopropyl benzene consumed in the reaction.

Example 4 Isopropyl benzene was vaporized and preheated to a temperature of about 440 C. and the preheated vapor was passed continuously into admixture with a stream of steam superheated'to about 1070 C. at such ratethat the temperature of the resultant mixture was approximately 900 C. The mixture was cooled and condensed immediately after -formation and the organic layer of condensate was separated, dried, and analyzed.

It contained 53 per cent by weight of styrene, 2

per cent of alpha-methyl styrene, and 8.3 per cent of phenylacetylene, the remainder being unreacted isopropyl benzene and by-products such as benzene and probably naphthalene.

Example 5 chlorobenzene and meta-chloro-ethylbenzene.

I have also pyrolyzed meta-ethyl-isopropyl benzene as hereinbeiore described to obtain a product comprising styrene homologues, e. g. meta-ethyl styrene, meta-divinyl benzene, etc., and arylacetylenes, e. g.-phenylacety1ene, metavinyl-phenylacetyle'ne, etc. The arylacetylenes in the mixture inhibited polymerization of the isopropyl benzene compounds such as ortho-, meta-,' or para-bromo-isopropyl benzene, 3-ch1oro-S-ethyl-isopropyl benzene, ortho-chloro-isopropyl benzene, para-methyl-isopropyl benzene, diethyl-isopropyl benzene, di-isopropyl benzene,

etc. may be pyrolyzed according to the invention to obtain a product comprising homologues or-analogues of'styrene and an arylacetylene.

Other nuclear substituted In the claims the term styrene-like compound" refers to a compound of the class consisting of styrene and its homologues and analogues,

Other modes of applying the principle of the invention may be employed instead of those explained, change being made as regards the meth- 0d herein disclosed, providedthe step. or steps stated by any of the following claims or the equivalent of such stated step or steps be employed.

I therefore particularly point out and distinctly .claim as my in ention:-.

1, A method for the simultaneous formation of a styrene-like compound and an arylacetylene which comprises pyrolyzing at a temperature o!v at least 750 C. a benzene derivative having thegeneral formula I 4 Y, wherein R represents an isopropyl or isopro'penyl radical, X and Y each represent hydrogen, halogen, or an alkyl radical containing not more than 3 carbon atoms, and n and 1 are integers having a sum not exceeding 5. r

v 2. A method for the simultaneous formation of a styrene-like compound and an arylacetylene which comprises heating to a pyrolyzing temperature of at least 750 C. and cooling sufllciently rapidly to avoid appreciable carbonization, a benzene derivative having the general I formula wherein R represents an isoprop'yl or iso'propenyl radical, x and Y each represent hydrogen, halogen, or an alkyl radical containing not more than 3 carbon atoms, and n and n are integers having,

a sumnot exceeding 3.

3; A method for the-simultaneous production of a styrene-like compound and an arylacetylene which comprises simultaneously passing separate streams of superheated steam and of a benzene derivative having the general formula 50 Y. wherein R represents an isopropyl or isopropenyl radical, X and Y each represent hydrogen, halogen or an alkyl radical containing not more than 3 carbon atoms, and n and n are integers having a sum not exceeding 5, into admixture to form a mixture having a temperature between 800 and 900 C. and promptly cooling the mixture to a temperature below 100" 0., the steam employed being superheated sufficiently to attain said pyrolysis temperature. I 4

4. A method for the simultaneous formation of styrene and phenylacetylene which comprises pyrolyzing isopropyl. benzene at a temperature of at least 750 C.

5. A method for the simultaneous formation of atyrene and phenylacetylene which comprises continuously passing isopropyl benzene into admixture with steam superheated sufliciently' so 

